Graphene for semiconductor co-doping boron and nitrogen at the same time and preparation method thereof

ABSTRACT

Disclosed are boron/nitrogen co-doped graphene for semiconductor applications and a method for producing the same. The boron/nitrogen co-doping allows the use of the doped graphene in a wider variety of applications, including semiconductors. In contrast, graphene structures produced by conventional methods have good physical, chemical, and electrical stability but cannot be used in semiconductor applications due to the absence of band gaps therein. In addition, the boron/nitrogen co-doping makes the doped graphene highly dispersible in organic solvents.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to boron/nitrogen co-doped graphene forsemiconductor applications and a method for producing the same.

2. Description of the Related Art

Carbon materials, such as fullerenes, carbon nanotubes, graphene, andgraphite composed of carbon atoms have attracted increasing attention inrecent years.

Particularly, research on carbon nanotubes and graphene is activelyunderway. Graphene can be formed on a large area and possesses highconductivity as well as good electrical, mechanical and chemicalstability. Due to these advantages, graphene is gaining particularinterest as a basic material for electronic circuits.

Graphene is a basic building block for graphite and is a thin film whosethickness corresponds to that of one carbon atom.

Graphene is a two-dimensional planar material consisting of covalentlybonded carbon atoms in a hexagonal arrangement. Graphene has excellentphysicochemical properties, a specific surface area as large as about2,000-3,000 cm²/g, and superior thermal and electrical conductivity.

Graphene production processes can be broadly classified into twoapproaches: bottom up and top down processes. According to arepresentative bottom up process, graphene is synthesized by chemicalvapor deposition and epitaxy of a carbon precursor on a suitablesubstrate, such as a metal or silicon substrate. This process enablesthe synthesis of high-quality graphene depending on reaction conditionsbut requires high temperatures for graphene synthesis. Another problemis that the yield of graphene is limited depending on the area of thesubstrate used.

Meanwhile, according to a representative top down process, planargraphite is oxidized, a sheet of graphene is exfoliated from theoxidized graphite, and the graphene oxide is reduced. Thisoxidation/reduction process uses a strong acid for the oxidation and astrong reducing agent for the reduction. However, the graphene structuredamaged by the oxidation is not fully recovered to its original stateeven after the reduction. Other examples of top down processes forgraphene production include edge exfoliation and ball milling. Accordingto the edge exfoliation process, edges of graphene sheets constitutinggraphite are selectively functionalized, followed by exfoliation.According to the ball milling process, graphene is isolated fromgraphite by mechanical exfoliation.

Graphene doping processes can be divided into physical doping andchemical doping. Physical doping is based on physical binding betweengraphene and doping agents and is thus susceptible to externalenvironmental factors. This susceptibility makes it difficult tocontinuously maintain the doping effects. In contrast, chemical dopingis based on chemical bonding between dissimilar elements and grapheneand is thus advantageous in continuously maintaining the doping effects.The physical properties of graphene vary depending on thecharacteristics of dissimilar elements introduced into graphene and canthus be controlled as desired by varying the amounts and kinds of thedissimilar elements.

On the other hand, graphene produced by the bottom-up or top-downprocess is a semi-metallic material with high electron mobility.However, the graphene cannot be applied to semiconductors for on/offcontrol in logic elements due to the absence of band gap therein. Thus,there is a continued need for research aimed at finding availablegraphene for semiconductor applications based on chemical doping.Despite this, such research is in its infancy.

As the prior art, Korean Patent Publication No. 10-2011-0016287 (“PatentDocument 1”) relates to a method for coating with graphene oxide.Specifically, a colloidal graphene oxide solution is directly coated onthe surfaces of various bases, dried, and thermally processed to formgraphene thin films on the bases. However, Patent Document 1 neitherdiscloses nor suggests a technique associated with the use of graphenein semiconductor applications by forming a band gap in the graphene.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aboveproblems, and it is an object of the present invention to providechemically doped graphene suitable for use in semiconductor applicationsand a method for producing the doped graphene.

According to one aspect of the present invention, there is providedboron/nitrogen co-doped graphene for semiconductor applications whereinthe doping is performed after an alkali metal in Group 1 of the PeriodicTable or an alkaline earth metal in Group 2 of the Periodic Table ischemically bonded to a carbon precursor.

The boron/nitrogen doping is performed using a boron precursor and anitrogen precursor and the boron precursor is a compound in which ahalogen selected from the group consisting of F, Cl, Br, and I is bondedto boron.

The boron precursor is selected from the group consisting of BF, BF₃,BCl₃, BBr₃, BI₃, and mixtures thereof and the nitrogen precursor isselected from the group consisting of N₂, NH₃, NF₃, NCl, NBr₃, NI₃,NHCl₂, NH₂Cl, NF₅, N₂F₄, N₂Cl₄, and mixtures thereof.

The carbon precursor is a compound in which a halogen selected from thegroup consisting of F, Cl, Br, and I is bonded to carbon.

The carbon precursor is selected from the group consisting of CF₄, C₂F₄,CF₆, CCl₄, C₂Cl₄, CCl₆, C₆Cl₆, CBr₄, C₂Br₄, C₆Br₆, CI₄, C₂I₄, C₆I₆, andmixtures thereof.

The graphene is doped with 0.01 to 5.00 at. % of boron and 0.01 to 5.00at. % of nitrogen.

The alkali metal is selected from the group consisting of lithium,sodium, potassium, rubidium, cesium, francium, and mixtures thereof andthe alkaline earth metal is selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, radium, and mixturesthereof.

The doped graphene has a band gap of 0.1 to 5 eV.

According to another aspect of the present invention, there is provideda method of producing doped graphene for semiconductor applications,including

-   -   1) adding a carbon precursor and an alkali metal or alkaline        earth metal to a closed container,    -   2) adding a boron precursor and a nitrogen precursor to the        closed container, and    -   3) raising the internal temperature of the closed container and        maintaining the temperature.

The boron precursor is a compound in which a halogen selected from thegroup consisting of F, Cl, Br, and I is bonded to boron.

The boron precursor is selected from the group consisting of BF, BF₃,BCl₃, BBr₃, BI₃, and mixtures thereof and the nitrogen precursor isselected from the group consisting of N₂, NH₃, NF₃, NCl, NBr₃, NI₃,NHCl₂, NH₂Cl, NF₅, N₂F₄, N₂Cl₄, and mixtures thereof.

The carbon precursor is a compound in which a halogen selected from thegroup consisting of F, Cl, Br, and I is bonded to carbon.

The carbon precursor is selected from the group consisting of CF₄, C₂F₄,CF₆, CCl₄, C₂Cl₄, CCl₆, C₆Cl₆, CBr₄, C₂Br₄, C₆Br₆, CI₄, C₂I₄, C₆I₆, andmixtures thereof.

In step 1), the carbon precursor and the alkali metal or alkaline earthmetal are added in amounts of 0.01 to 20% by volume.

According to the method of the present invention, 0.01 to 5.00 at. % ofboron and 0.01 to 5.00 at. % of nitrogen are co-doped into graphene.

In step 3), the internal temperature of the closed container is raisedto 50 to 400° C. and is maintained for 0.5 to 12 hours.

In step 1), the carbon precursor and the alkali metal or alkaline earthmetal are added in a total amount of 10 to 30% by volume, based on thevolume of the closed container.

The nitrogen/boron co-doping allows the use of the doped grapheneaccording to the present invention in a wider variety of applications,including semiconductors. In contrast, graphene structures produced byconventional methods have good physical, chemical, and electricalstability but cannot be used in semiconductor applications due to theabsence of band gaps therein. In addition, the nitrogen/boron co-dopingmakes the doped graphene of the present invention highly dispersible inorganic solvents.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a diagram showing the mechanism of co-doping of boron andnitrogen into a graphene structure;

FIG. 2 is a graph showing the band gap of doped graphene produced inExample 1, which was calculated by UV-Vis spectroscopy;

FIG. 3 is a current/voltage curve for a field-effect transistoremploying doped graphene produced in Example 1;

FIG. 4 shows images comparing the degrees of dispersion of graphenestructures produced in Example 1 and Comparative Examples 1 and 2.

FIG. 5 is a graph showing the decomposition temperatures of graphenestructures produced after reaction at different temperatures, which weremeasured in Experimental Example 4;

FIG. 6 is a graph showing the decomposition temperatures of graphenestructures produced after reaction for different times, which weremeasured in Experimental Example 5;

FIG. 7 shows scanning electron microscopy (SEM) images of graphenestructures produced in Example 1 and Comparative Examples 1 and 2;

FIG. 8 is a graph showing the results of elemental analysis of graphenestructures produced in Example 1 and Comparative Examples 1 and 2; and

FIG. 9 shows Raman spectra of graphene structures produced in Example 1and Comparative Examples 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

As a result of earnest and intensive research to develop graphene forsemiconductor applications, the present inventors have found thatgraphene co-doped with boron and nitrogen is suitable for use insemiconductor applications. The present inventors have also found amethod for producing the doped graphene. The present invention has beenaccomplished based on these findings.

Specifically, the present invention provides boron/nitrogen co-dopedgraphene for semiconductor applications wherein the doping is performedafter an alkali metal in Group 1 of the Periodic Table or an alkalineearth metal in Group 2 of the Periodic Table is chemically bonded to acarbon precursor.

The co-doping of graphene with boron and nitrogen enables the formationof a band gap in the graphene. As a result, the doped graphene can beused in semiconductor applications, which has previously been difficultto achieve. In addition, the graphene co-doped with both boron andnitrogen exhibits markedly improved dispersibility compared to graphenedoped with either boron or nitrogen.

The reason why the doping is performed after an alkali metal in Group 1of the Periodic Table or an alkaline earth metal in Group 2 of thePeriodic Table is chemically bonded to a carbon precursor is becauselarger amounts of boron and nitrogen can be doped. The chemical bondingis not particularly limited but is preferably covalent bonding.

The boron/nitrogen doping is performed using a boron precursor and anitrogen precursor. The boron precursor may be a boron halide but is notparticularly limited thereto. Preferably, the boron precursor is acompound in which a halogen selected from the group consisting of F, Cl,Br, and I is bonded to boron. More preferably, the boron precursor isselected from the group consisting of BF, BF₃, BCl₃, BBr, BI₃, andmixtures thereof. The nitrogen precursor is selected from the groupconsisting of N₂, NH₃, NF₃, NCl, NBr₃, NI₃, NHCl₂, NH₂Cl, NF₅, N₂F₄,N₂Cl₄, and mixtures thereof.

The carbon precursor may be a carbon halide but is not particularlylimited thereto. Preferably, the carbon precursor is a compound in whicha halogen selected from the group consisting of F, Cl, Br, and I isbonded to carbon. More preferably, the carbon precursor is selected fromthe group consisting of CF₄, C₂F₄, CF₆, CCl₄, C₂Cl₄, CCl₆, C₆Cl₆, CBr₄,C₂Br₄, C₆Br₆, CI₄, C₂I₄, C₆I₆, and mixtures thereof.

The graphene is doped with 0.01 to 5.00 at. % of boron and 0.01 to 5.00at. % of nitrogen. Within these ranges, a high band gap can be formed inthe doped graphene, allowing the use of the doped graphene insemiconductor applications and ensuring improved dispersibility of thedoped graphene.

The alkali metal is selected from the group consisting of lithium,sodium, potassium, rubidium, cesium, francium, and mixtures thereof andthe alkaline earth metal is selected from the group consisting ofberyllium, magnesium, calcium, strontium, barium, radium, and mixturesthereof.

The doped graphene of the present invention has a band gap of 0.1 to 5eV, which corresponds to that of a semiconductor. Accordingly, the dopedgraphene of the present invention can be used in semiconductorapplications.

In another aspect, the present invention provides a method of producingdoped graphene for semiconductor applications, including

-   -   1) adding a carbon precursor and an alkali metal or alkaline        earth metal to a closed container,    -   2) adding a boron precursor and a nitrogen precursor to the        closed container, and    -   3) raising the internal temperature of the closed container and        maintaining the temperature.

According to the method of the present invention, a band gap can beformed in graphene, which allows the use of the graphene insemiconductor applications.

The boron precursor may be a boron halide but is not particularlylimited thereto. Preferably, the boron precursor is a compound in whicha halogen selected from the group consisting of F, Cl, Br, and I isbonded to boron. More preferably, the boron precursor is selected fromthe group consisting of BF, BF₃, BCl₃, BBr₃, BI₃, and mixtures thereof.The nitrogen precursor is selected from the group consisting of N₂, NH₃,NF₃, NCl, NBr₃, NI₃, NHCl₂, NH₂Cl, NF₅, N₂F₄, N₂Cl₄, and mixturesthereof.

The carbon precursor may be a carbon halide but is not particularlylimited thereto. Preferably, the carbon precursor is a compound in whicha halogen selected from the group consisting of F, Cl, Br, and I isbonded to carbon. More preferably, the carbon precursor is selected fromthe group consisting of CF₄, C₂F₄, CF₆, CCl₄, C₂Cl₄, CCl₆, C₆Cl₆, CBr₄,C₂Br₄, C₆Br₆, CI₄, C₂I₄, C₆I₆, and mixtures thereof.

In step 1), the carbon precursor and the alkali metal or alkaline earthmetal are preferably added in amounts of 0.01 to 20% by volume. Withinthis range, doping of graphene with sufficient amounts of boron andnitrogen can be induced after the alkali metal or alkaline earth metalis chemically bonded to the carbon precursor.

According to the method of the present invention, 0.01 to 5.00 at. % ofboron and 0.01 to 5.00 at. % of nitrogen are co-doped into graphene.

In step 3), it is preferred to raise the internal temperature of theclosed container to 50 to 400° C. and maintain the temperature for 0.5to 12 hours. This temperature profile enables doping of graphene withlarger amounts of boron and nitrogen.

In step 1), the carbon precursor and the alkali metal or alkaline earthmetal are preferably added in a total amount of 10 to 30% by volume,based on the volume of the closed container.

The present invention will be explained in detail in such a manner thatthose with ordinary knowledge in the art can easily carry out theinvention with reference to the following preferred embodiments. Thepresent invention may, however, be embodied in many different forms andis not limited to the embodiments as set forth herein.

EXAMPLES Example 1

4 ml of carbon tetrachloride (CCl₄) and 7.6 g of potassium (K) were putin an autoclave and 0.39 ml of boron tribromide (BBr₃) was introducedinto the autoclave under a nitrogen atmosphere. The mixture was heatedat 270° C. for 30 min to produce graphene flakes co-doped with 2.38 at.% of boron and 2.66 at. % of nitrogen. FIG. 1 shows the mechanism of theproduction of the doped graphene and an image of the doped graphene.

COMPARATIVE EXAMPLES Comparative Example 1

Graphene flakes were produced in the same manner as in Example 1, exceptthat the boron precursor was not introduced.

Comparative Example 2

Graphene flakes were produced in the same manner as in Example 1, exceptthat the nitrogen atmosphere was changed to an argon atmosphere.

EXPERIMENTAL EXAMPLES Experimental Example 1 Band Gap Measurement

The band gap of the graphene flakes produced in Example 1 was measuredby UV-Vis spectroscopy. The results are shown in FIG. 2.

As shown in FIG. 2, the band gap of the nitrogen/boron co-doped graphenewas calculated to be 3.3 eV, which is sufficiently higher than the bandgaps of undoped graphene (0 eV) and conventional doped graphenestructures (≦3.0 eV). The results of the experiment indicated that thedoped graphene can be used for on/off control and has semiconductorproperties, which can be explained by its high band gap.

Experimental Example 2 Measurement of Semiconductor Properties UsingField-Effect Transistor

A field-effect transistor was fabricated using the boron/nitrogenco-doped graphene of Example 1. A current/voltage curve was plotted fora field-effect transistor to make sure whether the doped graphene showedsemiconductor properties. The results are shown in FIG. 3.

Experimental Example 3 Measurement of Degrees of Dispersion

An experiment was made to determine whether the boron/nitrogen co-dopedgraphene of Example 1 was more effectively dispersed inN-methyl-2-pyrrolidone (NMP) as an organic solvent than the graphenestructures of Comparative Examples 1-2. For this experiment, the degreesof dispersion of the graphene structures were measured after dipping inthe organic solvent for 2 months. The results are shown in FIG. 4.

FIG. 4 shows that the doped graphene of Example 1 (FIG. 4 a) was stablydispersed for 2 months, while the graphene structures of ComparativeExamples 1 (FIG. 4 b) and 2 (FIG. 4 c) were unstably dispersed for 2months. From these results, it can be confirmed that the doped grapheneof Example 1 possessed better dispersibility than the graphenestructures of Comparative Examples 1-2, demonstrating suitability of thedoped graphene of Example 1 for semiconductor applications compared tothe graphene structures of Comparative Examples 1-2.

Experimental Example 4 Graphene Structures Produced at DifferentReaction Temperatures

Graphene structures were produced in the same manner as in Example 1,except that the temperature of the autoclave was changed. Thedecomposition of the graphene structures and the graphene structure ofExample 1 was observed. The results are shown in FIG. 5.

As shown in FIG. 5, more desirable results were obtained in thetemperature range of 50-400° C. Particularly, the graphene was judged tobe thermally stable when it underwent less weight loss with increasingtemperature. FIG. 5 shows good thermal stability of the grapheneproduced after reaction at 270° C.

Experimental Example 5 Graphene Structures Produced for DifferentReaction Times

Graphene structures were produced in the same manner as in Example 1,except that the reaction time was changed while maintaining thetemperature of the autoclave. The results are shown in FIG. 6.

As shown in FIG. 6, the graphene structures began to form after 30 minfollowing the reaction, which was monitored through their thermalstability and electron microscopy. The graphene structure formed afterreaction for 12 h showed similar results to that formed after reactionfor 0.5 h. From these observations, it was concluded that it ispreferable to maintain the elevated temperature for 0.5-12 h. FIG. 6shows that the graphene structure formed after reaction for 0.5 h showedmore desirable results than that formed after reaction 1 h.

Experimental Example 6 Other Measurement Results and Degrees of Doping

FIG. 7 shows scanning electron microscopy (SEM) images of the graphenestructures produced in Example 1 (FIG. 7 a), Comparative Example 1 (FIG.7 b), and Comparative Example 2 (FIG. 7 c).

FIG. 8 is a graph showing the results of elemental analysis of thegraphene structures produced in Example 1 (BCN-graphene) and ComparativeExamples 1 (C-graphene) and 2 (BC-graphene). The constituent elements ofthe graphene flakes were analyzed by X-ray photoelectron spectroscopy(XPS).

Table 1 shows the contents of the elements of the graphene structuresproduced in Example 1 and Comparative Examples 1-2.

TABLE 1 C B Br Cl N O Sample (at. %) (at. %) (at. %) (at. %) (at. %)(at. %) C/B C/N C-graphene 92.46 BDL^(a) BDL^(a) 1.05 0.59 5.90 NA^(b)182.2 BC-graphene 87.47 BDL^(a) 0.28 1.28 0.73 10.07 NA^(b) 139.7BCN-graphene 84.41 2.38 BDL^(a) 1.07 2.66 9.47 31.9 37.0 ^(a)BDL = Belowdetection limit or not available. ^(b)NA = Not applicable.

FIG. 9 shows Raman spectra of the graphene structures (Example 1:BCN-graphene, Comparative Example 1: C-graphene, Comparative Example 2:BC-graphene).

The constituent elements of the graphene flakes produced in Example 1and Comparative Examples 1-2 were analyzed by X-ray photoelectronspectroscopy (XPS). The results are shown in FIG. 8. Peaks correspondingto boron and nitrogen were observed in the boron/nitrogen co-dopedgraphene of Example 1. The contents of the individual elements wereprecisely calculated from FIG. 9.

The preferred embodiments of the present invention have been describedherein, but the scope of the present invention is not limited thereto.It should be understood that various modifications are possible withoutdeparting from the spirit of the invention and such modifications areintended to come within the scope of the appended claims.

What is claimed is:
 1. Boron/nitrogen co-doped graphene for semiconductor applications wherein the doping is performed after an alkali metal in Group 1 of the Periodic Table or an alkaline earth metal in Group 2 of the Periodic Table is chemically bonded to a carbon precursor.
 2. The boron/nitrogen co-doped graphene according to claim 1, wherein the boron/nitrogen doping is performed using a boron precursor and a nitrogen precursor and the boron precursor is a compound in which a halogen selected from the group consisting of F, Cl, Br, and I is bonded to boron.
 3. The boron/nitrogen co-doped graphene according to claim 1, wherein the boron precursor is selected from the group consisting of BF, BF₃, BCl₃, BBr₃, BI₃, and mixtures thereof and the nitrogen precursor is selected from the group consisting of N₂, NH₃, NF₃, NCl, NBr₃, NI₃, NHCl₂, NH₂Cl, NF₅, N₂F₄, N₂Cl₄, and mixtures thereof.
 4. The boron/nitrogen co-doped graphene according to claim 1, wherein the carbon precursor is a compound in which a halogen selected from the group consisting of F, Cl, Br, and I is bonded to carbon.
 5. The boron/nitrogen co-doped graphene according to claim 1, wherein the carbon precursor is selected from the group consisting of CF₄, C₂F₄, CF₆, CCl₄, C₂Cl₄, CCl₆, C₆Cl₆, CBr₄, C₂Br₄, C₆Br₆, CI₄, C₂I₄, C₆I₆, and mixtures thereof.
 6. The boron/nitrogen co-doped graphene according to claim 1, wherein the graphene is doped with 0.01 to 5.00 at. % of boron and 0.01 to 5.00 at. % of nitrogen.
 7. The boron/nitrogen co-doped graphene according to claim 1, wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, francium, and mixtures thereof and the alkaline earth metal is selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, radium, and mixtures thereof.
 8. The boron/nitrogen co-doped graphene according to claim 1, wherein the doped graphene has a band gap of 0.1 to 5 eV.
 9. A method of producing doped graphene for semiconductor applications, comprising 1) adding a carbon precursor and an alkali metal or alkaline earth metal to a closed container, 2) adding a boron precursor and a nitrogen precursor to the closed container, and 3) raising the internal temperature of the closed container and maintaining the temperature.
 10. The method according to claim 9, wherein the boron precursor is a compound in which a halogen selected from the group consisting of F, Cl, Br, and I is bonded to boron.
 11. The method according to claim 9, wherein the boron precursor is selected from the group consisting of BF, BF₃, BCl₃, BBr₃, BI₃, and mixtures thereof and the nitrogen precursor is selected from the group consisting of N₂, NH₃, NF₃, NCl, NBr₃, NI₃, NHCl₂, NH₂Cl, NF₅, N₂F₄, N₂Cl₄, and mixtures thereof.
 12. The method according to claim 9, wherein the carbon precursor is a compound in which a halogen selected from the group consisting of F, Cl, Br, and I is bonded to carbon.
 13. The method according to claim 9, wherein the carbon precursor is selected from the group consisting of CF₄, C₂F₄, CF₆, CCl₄, C₂Cl₄, CCl₆, C₆Cl₆, CBr₄, C₂Br₄, C₆Br₆, CI₄, C₂I₄, C₆I₆, and mixtures thereof.
 14. The method according to claim 9, wherein, in step 1), the carbon precursor and the alkali metal or alkaline earth metal are added in amounts of 0.01 to 20% by volume.
 15. The method according to claim 9, wherein 0.01 to 5.00 at. % of boron and 0.01 to 5.00 at. % of nitrogen are co-doped into graphene.
 16. The method according to claim 9, wherein, in step 3), the internal temperature of the closed container is raised to 50 to 400° C. and is maintained for 0.5 to 12 hours.
 17. The method according to claim 9, wherein, in step 1), the carbon precursor and the alkali metal or alkaline earth metal are added in a total amount of 10 to 30% by volume, based on the volume of the closed container. 